It is known to provide an electromagnet of a type which has a coil surrounding a pole with an external magnetic circuit enclosing the coil and usually partly enclosing the pole with one or more end pole pieces. In one known actuating magnet of this general type, the outer cover which forms the magnetic exciting circuit is formed of two prismatically curved or U-shaped stator laminations which are welded together with the pole plate and these are mounted within the cover. An actuating magnet having a magnetic circuit cover of this type is costly to manufacture and occupies considerable space since, seen transversely, the square area enclosed within the cover corresponds, at a minimum, to the outer diameter of the coil. A structure of this type is shown in Swiss Pat. No. 517,997.
U.S. Pat. No. 1,556,363 shows an electromagnetic device having an outer housing which is square in transverse cross-section with a pole plate inserted on one side and held against rotation by means of closed recesses in the cover, and it is also held in the axial direction. The pole plate at the other end is U-shaped in transverse cross-section, the turned-down shanks of the pole plate engaging recesses in the cover. The position of the pole plate on the cover is also assured by means of a pivot pin. An armature is disposed between the pole plate and the coil where it is pivotable about the pivot pin. The actuating magnet structure is of extremely complicated configuration and can be manufactured only at great cost.
In yet another known actuating magnet structure, the cover or housing likewise consists of two U-shaped parts which are either connected tightly by means of the pole plates, the parts of the cover projecting axially over the pole plates and being plastically deformed by rivet jointing. This is shown in German Offenlengungsschrift No. 14 89 975.